1. Field of the Invention
The present invention relates to a mixing faucet that is mounted to a bathroom spigot or the like and can discharge freely hot and cold water by mixing hot water and cold water, and more specifically relates to a mixing faucet that maintains the temperature of mixed water at a predetermined temperature by modifying the proportion between opening areas of hot water inlet openings and cold water inlet openings by displacing a valve body using a temperature sensing spring the elastic force of which changes in accordance with changes in the temperature of mixed water flowing inside.
2. Description of the Related Art
Known conventional mixing faucets include (for instance, JP 2006-307971 A) a mixing faucet wherein a hot water inlet opening and a cold water inlet opening are opened in succession, spaced apart in the axial direction, in the peripheral wall of a bottomed tubular casing, from the bottom toward an opening side that constitutes an outlet opening; a control valve element slidably disposed inside the casing is brought to a balanced state by being wedged between a bias spring and a temperature sensing spring in the form of an SMA (shape memory alloy) spring; and the properties of the SMA spring are exploited in such a manner that when there rises the temperature of mixed water, being a mixture of hot water and cold water, the biasing force of the SMA spring on the control valve element is increased, whereby the balance with the bias spring is upset and the opening area of the hot water inlet opening is reduced, and the control valve element slides so as to increase the opening area of the cold water inlet opening; and conversely, when the temperature of mixed water drops, the biasing force of the SMA spring on the control valve element is reduced, whereby the balance with the bias spring is upset and the opening area of the hot water inlet opening is increased, and the control valve element slides so as to reduce the opening area of the cold water inlet opening; so that, as a result of the foregoing, the mixed water was kept at a predetermined temperature.
The mixing faucet using an SMA spring as a temperature sensing spring is problematic in that in a cold water discharge state, arrived at through closing of the hot water inlet opening and opening of the cold water inlet opening alone by means of the control valve element, the temperature of cold water flowing through the interior drops, as a result of which the elastic force of the SMA spring decreases, and thus the hot water inlet opening is harder to close. In the mixing faucet of JP 2006-307971 A, a pull-up spring is provided in the bottom side within the casing, so that the decrease in elastic force of the SMA spring that accompanies a drop in the water temperature is compensated through the action of the biasing force of the pull-up spring on the control valve element during a cold water discharge state.
The mixing faucet using an SMA spring as a temperature sensing spring was advantageous in that it afforded a compact mixing faucet since the SMA spring by itself functions as an actuator, but was problematic in terms of cost, since the material of the SMA spring is expensive. Costs can be significantly cut by reducing the wire diameter and the number of turns of the SMA spring as much as possible, but SMA springs have a weaker biasing force than ordinary coil springs, and there are also limitations to the extent to which wire diameter and number of turns can be reduced.